Evaluation of Month of Birth in Neuromyelitis Optica Spectrum Disorders (NMSOD) and Multiple Sclerosis (MS)

INTRODUCTION: Multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMO) are chronic immune-mediated diseases in the central nervous system (CNS). Environmental factors such as month of birth can be a trigger for these diseases. Therefore, we conducted this study to compare the months of birth in MS and NMOSD patients with the control group. METHODS: In this cross-sectional study, 2345 patients with MS, 220 NMOSD patients, and 2174 healthy subjects were enrolled. Demographic information such as age, sex, month of birth, and education in three groups was extracted from the database. The associations between month of birth and MS were studied by binary logistic regression with adjusting for the year of birth. RESULTS: There was a reduced birth rate in September-October in NMOSD (OR = 0.309, 95% CI: 0.150-0.636; p < 0.001) and MS patients (OR = 0.470, 95% CI: 0.374-0.591; p < 0.001) compared to the general population. The birth rate in March-April in MS was higher than the control group (OR = 1.613, 95% CI: 1.324-1.964; p < 0.001). There was no difference in the birth month distribution between the NMOSD and MS patients. No significant difference in MOB among different MS types was found. CONCLUSION: Our findings showed a decreasing risk of NMOSD and MS in individuals born in the autumn months and an increasing MS risk in spring. More studies are required to elucidate the association between the month of birth and risk of MS and NMOSD and the seasonality factors.